1. Field of the Invention
The present invention relates to a microscope arrangement for inspecting a substrate, such as a semiconductor wafer, a flat panel, a mask or reticle.
2. Description of the Related Art
In order to produce integrated circuits, semiconductor substrates, masks or reticles, for example, are subject to a number of processes in which layers are respectively applied, structured or remodeled. During or between these processes, it is possible for the structures formed on the semiconductor or glass substrate to be damaged or, for disadvantageous impurities to be detected on the substrate due to increased particle formation with subsequent deposition on the substrate. In order to detect defects to the substrate or particle formations on the substrate, and to be able, in the case of detection, to institute preventive measures for subsequently produced substrates, inspections for defects and particles are carried out regularly between the respective processes.
The aim of such an inspection is to classify the particle deposition or the defect in order to be able to investigate the respective cause of the problem more accurately. The aim is also to reach a decision on further processing of the relevant substrate. Thus, for example, consideration could also be given to adding a cleaning step cleaning step or complete rejection of the substrate.
Classification of the particle or defect requires high-resolution microscopy. However, regular inspection covering all the structures on the substrate with the aid of a high-resolution microscope would slow down the production process substantially and thus lead to an increase in costs. Since a large portion of the defects and particles can be detected macroscopically, i.e., with the naked eye or with the aid of a simple sight glass, the inspection step in the fabrication of semiconductor products or masks/reticles is usually divided into two substeps.
In a first substep, an oblique light inspection is carried out, i.e., the substrate is observed by the operating staff under obliquely incident light through the sight glass at a first work station comprising an illuminating system and a sight glass having, for example, a magnifying glass. The sight glass comprises, if appropriate, an integrated reversible magnification. For example, the angle of incidence of the incident light on the substrate surface is varied manually in this case. Because the incident light is re-emitted by the substrate either in the direction of a diffractive order or the mirror reflection, diffusely reflecting particles on the surface of the substrate become particularly visible to the operator. Upon completion of this first step, the operator compiles in electronic form or on paper a report of the visual examination, specifying the type of particle or defect detected, as well as its position on the substrate.
The second substep includes evaluating the report compiled in the first substep in relation to the position of the defect or particle on the substrate at a second work station employing a high-resolution microscope. Since there is no exact coordinate grid available through the sight glass during the manually performed oblique light inspection, the positional data are naturally imprecise and frequently affected by error. Finding the relevant position of the defect or particle on the substrate in the high-resolution microscope likewise rests on the subjective judgment of the position datum by the operator of the microscope. Accordingly, a positional determination may need to be carried out anew in this step.
Moreover, a further disadvantage arises from the fact that the data transfer in the report and the transportation of the substrate from the first work station to the second work station entail increased outlay on time and costs as well as susceptibility to error.